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NEW YORK — Nearly all of today's Native Americans in North, Central and South America can trace their ancestry to just six women whose descendants immigrated around 20,000 years ago, a DNA study suggests.

The result doesn't mean that only six women gave rise to the migrants who crossed into North America from Asia in the initial populating of the continent.

Rather, it suggests that only six left a particular DNA legacy that persists to today in about about 95 percent of Native Americans, said study co-author Ugo Perego in Utah.

The women didn't necessarily arrive together, nor even all live at the same time, he said. Results indicate the women arrived sometime between 18,000 and 21,000 years ago.

Find out how scientists decode our DNAThe work was published this week by the journal PLoS One. Perego is from the Sorenson Molecular Genealogy Foundation in Salt Lake City and the University of Pavia in Italy.

The work confirms previous indications of just six maternal lineages, as well as a date of around 20,000 years ago for when the first people in North America arrived after crossing a land bridge from Asia, Perego said.

The researchers studied mitochondrial DNA, which is passed only from mother to daughter. They created a "family tree" that traces the different DNA lineages found in today's Native Americans. By noting mutations in each branch and applying a formula for how often such mutations arise, they calculated how old each branch was. That indicated when each branch arose in a single woman.

The six "founding mothers" apparently did not live in Asia because the DNA signatures they left behind aren't found there, Perego said. So they probably lived in Beringia, the now-submerged land bridge that stetched to North America, he said.